ANSER (Alpha Vulpeculae). Tucked in between Albireo in Cygnus
and the ancient constellation Sagitta
is the little modern constellation Vulpecula, the Fox. The name is a shortened version of
the original, "Vulpecula cum Ansere," meaning "the Little Fox with
the Goose," the reason for the shortening quite obvious. The
brightest star (here the Alpha star) is set off a bit to the west
of the "W" that makes the most obvious part of the faint
constellation, and with the name "Anser" seems to represent the
dropped part of the constellation's name, though there is little
authority for it but some obscure references in dictionaries. Even
as the constellation's luminary, the star just barely makes fourth
magnitude (4.44). Unlike most of the cooler naked eye stars, which
are orange class K
giants, Anser is a class M (albeit warm M, class
M0) giant with a relatively cool temperature of only 3850 Kelvin.
From its rather large distance of 297 light years, and allowing for
a considerable amount of infrared radiation from its cool surface,
we find a luminosity 390 times that of the Sun and a resulting large radius of 45 times
solar. Given the inevitable errors of measurement of small values,
this figure agrees well with the radius of 53 solar derived from
distance and a direct measure of angular diameter. A radius of 50
times that of the Sun would make the star almost half an
astronomical unit across and nearly two-thirds the size of
Mercury's orbit. With a mass around 1.5 times that of the Sun,
Anser may (uncertainly) still be in the act of brightening with a
dead helium core that has yet to fire up and fuse to carbon, after
which it will dim a bit and settle down for a time as one of those
class K orange giants. On the other hand, it might also be
brightening for the
second time with a
dead carbon-oxygen core. A high nitrogen content almost double that
of the Sun suggests that by-products of thermonuclear fusion (from
a hydrogen-fusing shell around the dead core) are reaching the
surface. On the other hand, the heavier metal content is down,
iron coming in at about two-thirds solar. The star is sometimes
listed as having a companion. Following a system of star names
that originated with the careful 18th century observations of John
Flamsteed, Anser is also called 6 Vulpeculae. With binoculars, a
fifth magnitude star, 8 Vulpeculae (a class K giant), is seen about
7 minutes of arc (0.12 degree) away. The apparent duplicity is
only a line-of-sight coincidence, however, as 8 Vulpeculae lies 485
light years away, 60 percent farther than Anser. An older
suggestion that there might be a much closer companion that is not
directly separable from Anser proper remains unresolved.